It is the primary aim of the proposed research to more clearly define those events which occur during the development of normal thymus derived lymphocytes (T-cells) and leukemic T-cells. Thymic epithelial cell cultures and/or products from the thymus will be used to study the sequential development of precursor cells from normal and leukemic animals into T-cells. These cells will be examined for the acquisition of, or changes in surface markers, reactivity to mitogens, migration patterns and functional properties. Morphological studies will be carried out using electron microscopy and surface markers to correlate molecular events with ultrastructural changes. The proposed research will allow us to correlate these characteristics of normal and leukemic T-cells to a particular stage of cell differentiation.